Organic EL panels that include organic electroluminescent elements utilizing electroluminescence of organic materials have received attention. Organic EL elements emit light by recombining holes injected from the anode and electrons injected from the cathode within a light-emitting layer disposed between these electrodes. When used as display panels for thin-profile display devices, such organic EL panels are superior to liquid crystal display devices in terms of high contrast ratio and low power consumption, for example. Also, organic EL panels are expected to be applied to various fields including illumination devices in addition to display devices.
For use in the fields such as display devices, organic EL panels are required to emit various colors of light, and are strongly desired to have an organic EL element structure capable of emitting white light. Various organic EL element structures capable of emitting white light have been developed. For example, an element structure called tandem structure is known which drives organic EL elements stacked in the vertical direction with a single power source. Although common tandem structures include organic EL elements that emit the respective primary colors of light, a tandem structure is also known which includes a stack of organic EL elements that emit white light (for example, see Patent Literature 1).
Other known element structures include an element structure in which light-emitting layers for the respective colors are stacked adjacent to each other (for example, see Patent Literature 2) and an element structure which contains two or more luminescent dopant materials with different emission peak wavelengths in one light-emitting layer (for example, see Patent Literature 3).